Field of the Invention
The present invention pertains to guided missiles and concerns a gas propulsion unit using a solid propellant and comprising several side nozzles, the relative flow-rates of which can be controlled in order to modify the missile's flight trajectory.
The maneuvering capacity of offensive targets is being constantly improved, thus increasing interception error and error in computing flight distances for missiles. When firing a missile, consideration must be given to the cruising stage when it is desirable to maintain the speed at which the missile moves, and the final stage when the measured trajectory error should be cancelled or at least reduced to a value compatible with the range of effectiveness of the military payload, which may be nil in the case of a hollow-shaped charge.
Description of the Prior Art
Several types of guided missiles, therefore, have homing means to deflect the trajectory of the missile. These means comprise a gas propulsion unit using solid propellant to feed several nozzles. It is, therefore, possible in the prior art to deflect a flight trajectory by controlling the relative flow-rates of the gas jets given by a set of nozzles carefully arranged on the periphery of the missile's body. It is also possible, in the prior art, to tilt the nozzles towards the rear of the missile in order to create a longitudinal thrust in conjunction with a lateral thrust.
A difficulty inherent in the use of solid propellants results from the fact that, once combustion has completely begun, the combustion pressure must be contained within relatively narrow limits. A drop in combustion pressure, resulting from an excessive gas flow-rate, leads to the extinguishing of the propulsion unit. Conversely, an increase in combustion pressure resulting from a reduction in gas flow-rates, causes the untimely explosion of the propulsion unit.
Guidance propulsion units using solid propellants may be divided into several distinct classes, depending on the operating mode of the means used to regulate the relative flow-rate of the gas streams from the nozzles. In one class, as described in the U.S. Pat. No. 4,017,040, each pair of diametrically opposite nozzles is fitted with a valve that has three stable positions: an initial position, a second one for which the gas flows are respectively directed into the first and second nozzles, and a third position in which the gas flow-rate is distributed equally between the two nozzles. In another class, illustrated by the device described in the French patent application No. 2 538 098, each pair of nozzles is fitted with a valve that has two stable positions and operates according to an alternating "all or nothing" cycle. By varying the cyclical opening ratio of the valve, the gas flow may be distributed as desired between either of the two diametrically opposite nozzles.
In these propulsion devices, given the design of the means used to open and shut the valve opening, and for a number of nozzles equal to four or more, it is not possible to obtain all the theoretically possible combinations for opening or shutting the nozzles. A device of this kind is described in the French patent application published under No. 2 508 414. This device comprises a power source providing a gas flow to a set of fixed nozzles set in an annular element within which movable jackets are arranged coaxially. Each of these jackets is provided with a set of apertures for the gases to pass through. The apertures are arranged in such a way, that, through the mobility of the jackets with respect to one another and with respect to the annular element, any one of the nozzles may be supplied. Means are, therefore, provided to position the apertures so that they face the inlet holes of the nozzles.
Several disadvantages have been noted in this respect. There is no system capable of keeping all the nozzles shut. The imperviousness of the mobile elements to one another has to be provided by gaskets and is therefore not perfect. High pressure results in rapid clogging. Furthermore, installation is cumbersome and, therefore, expensive.